Moss Tank
A Moss Tank is a type of independent, self-supporting spherical cargo tank used on gas carriers, especially LNG carriers, developed by the Norwegian company Moss Maritime. The spheres — typically four or five in a row — sit in the hull supported at their equator, with the upper half rising above deck as the familiar domes that make Moss-type LNG ships instantly recognisable.
The spherical shape is very strong and distributes stress evenly, and each tank is a fully independent structure with its own insulation, so a leak is contained by the tank itself rather than relying on the hull. Moss tanks are one of the two main containment families, the other being membrane systems.
The Moss spherical tank is a robust, well-proven containment design whose independence and strength give it a strong safety record, at the cost of using the hull volume less efficiently than membrane tanks. The choice between Moss and membrane is one of the defining decisions in specifying an LNG carrier.
Why do some LNG carriers have visible spherical domes?
Those are the tops of Moss-type spherical cargo tanks, which sit in the hull with their upper halves projecting above the deck. The spherical shape is very strong and each tank is fully independent.